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The Homework Support files IntList.java, IntListVisitor.java, LengthVisitor, ScalarProductVisitor, and IntListTest.java provide a starting point for your code.   Feel free to edit these files and omit files that are not needed in this homework assignment.

Problems

Apply the visitor design pattern to define visitor classes implementing the IntListVistor interface IntList and its subclasses given above to formulate all of the following methods as  visitorsJUnit test class, IntListTest to test all of your new methods in the IntList class.  Use the LengthVisitor example as a guide for defining your new visitor classes.  Augment the test clas IntListTest.java to include test methods for each of your visitor classes.  Confine your documentation to writing contracts (purpose statements in HTDP terminology) for each visitor using javadoc notation (a comment preceding the corresponding definition) beginning  with /** and closing  with */ for each visitor class.  Use the documentation of LengthVisitor in the Homework Support files as an example.

• (10 pts.) boolean contains(int key)  returns true if key is in the list, false otherwise.  Name you visitor class ContainsVisitor.)
• (10 pts.) int reverse() constructs a list that is the reversal of this. Name your visitor class ReverseVisitor.  Hint: this computation is faster and simpler if you introduce a help "method" that takes an argument (also a visitor).
• (10 pts.) int sum()  computes the sum of the elements in the list.  Name your visitor class SumVisitor.
• (10 pts.) double average() computes the average of the elements in the list; returns 0 if the list is empty.
    Name your visitor class AverageVisitor.  Hint: you can cast an int to double by using the prefix casting operator (double).  
• (10 pts.) IntList notGreaterThan(int bound) returns a list of elements in this list that are less than or equal to bound .  Name your visitor class NotGreaterThanVisitor.
• (10 pts.) IntList remove(int key) returns a list of all elements in this list that are not equal to key.  .Name your visitor class RemoveVisitor
• (10 pts.) IntList subst(int oldN, int newN)  returns a list of all elements in this list with oldN replaced by newN.  Name your visitor class SubstVisitor
• (15 pts.) IntList merge(IntList other) merges this list with the input list other, assuming that this list and other are sorted in ascending order. Note that the lists need not have the same length.
  . Name your visitor class MergeVisitor.  Hint: add a method "method" mergeHelp(ConsIntList other) that does all of the work if one list is non-empty (a ConsIntList). Only mergeHelp is recursive. Use dynamic dispatch on the list that may be empty. Recall that a.merge(b) is equivalent to b.merge(a).  You can formulate help methods as visitors.
• (15 pts.) IntList mergeSort().  Leveraging the merge "method" you just wrote (as a visitor), write mergeSort() that sorts an IntList.  Recall that you need to write a help function that splits a list approximately in two.